Uni-directional



Dec. 1, 1964 R. D. DREW 3,159,431

METHQD AND APPARATUS FOR AUTOMATIC PROCESS CONTROL Filed April 20. 1962 4 Sheets-Sheet 2 UNI-DIRECTIONAL VALVE 7 5 65- PRESSURE waz mmwaa 6'6 PROCESS CHAMBER F/G 3 UNI-DIRECTIONAL VALVE PRESSURE RECORDING APPARATUS "78 86 o G SIMPLIFIED CIRCUIT DIAGRAM OF THE FLUCTUATION DETECTOR UNI-DIRECTIONAL UNI-DIRECTIONAL i u g gncx RESISTANCE umg e acx RESISTANCE men RESISTANCE -1%%*%?5%%%J D FLUCTUATING BETWEE N V LOWLEAKAGE LOW LEAKAGE TYPE TYPE cAmcnoR CAPACITOR men RESISTANCE 82 o.c.voLTMETER-e- INVENTOR.

RANGE O-ZOVOLTS 9056/) 0. Drew A ffomey RFD. DREW 3,159,431

METHOD AND APPARATUS FOR AUTOMATIC PROCESS CONTROL Dec. 1, 1964 4 Sheets-Sheet 5 Filed April 20, 1962 INVENTOR.

Robe/f 0. Drew Alfomey Dec. 1, 1964 R. D. DREW 3,159,431

METHOD AND APPARATUS FOR AUTOMATIC PROCESS CONTROL Filed April 20. 1962 4 Sheets-Sheet 4 79 70 CONVERTER l CONVERTER 46 HEATER IN VEN TOR R006 0. Drew Al omey point results in undesirable increase in attrition.

United States Patent 3,15%431 METHQD AND APPARATUS FUR AUTGMATKC PRQQESS NTROL Robert D, Drew, Wenonah, N.J., assignor to Socony Mobil Oil Company, Inc, a corporation of New York Filed AprJZti, 1%2, Ser. No. 189,115

4'Claims (Cl. Mil- 35) This invention relates to a means and method for controlling a process zone emitting 'a fluctuating signal, which signal may be a temperature, pressure, thickness of continuous metal strip, foil, etc. Theinvention provides instruments for and a method for measuring magnitude of fluctuation in afunction" and further applying'the measured magnitude of fluctuation obtained by these instruments to the control of the process.

The invention has particular applicability with respect to the TCC or moving bed process for the conversion of heavy hydrocarbons" to lighter products, such as gases and liquid fuels. In this process a granular catalyst is gravitated as a substantially compact mass of particles through a series of vesselswherein it is contacted with various gases and vapors. This catalyst is transferred from the bottom of the mass or column to the lower end of a pneumatic lift. In the lift the particles are carried in a rapidly moving stream of lift gas through a lift pipe and deposited from the upper end of the lift into a large separator. The particles then flow from the bottom of the separator in compact gravitating form to maintain the bed of catalyst in the various processing vessels. The static pressure in the lift pipe varies continually with time and isa function undergoing fluctuation in this process.

The critical features of catalyst velocity control in pneumatic lifts have been developed and are described in the literature. It is suflicient to state that there is a minimum pressure drop across the lift for any given set of conditions which produces minimum attrition or breakage of the catalyst during transfer through the lift and that this point can be found by reducing the total air to the lift until the pressure drop across the lift reaches a minimum and commencesto increase with further gas reduction. While these facts are well known now, it is difficult to continuously maintain a pneumatic lift in operation at the point of minimum attrition because of slight changes in gas flow, temperature, pressure, etc. which occur in the process. The lift tends to drift from the point of minimum attrition and any movement from this Unfortunately, this drift is diflicult to recognize and un-.v necessary catalyst damage occurs long before the shift can be recognized. i

This invention is based in part on the observation that the fluctuation of a main variable, such as the pressure in a pneumatic lift pipe, is often a better indication of the stability of the operating conditions than the main variable itself. \Vnen upsets are beginning to take place, the fluctuation of the mainvariable often increases before the absolutevalue of the variable starts to change apprech,

ably; Also, the ratio of fluctuation of the main variable tothe value of the main variable is often so small that it does not even appear on the recorder or'indicators used tunate since the detection of the fluctuation of the main to measure the main variable. This is decidedly unfor 3,159,431 Patented Dec. 1, 1964 ice an approaching upset in liftconditions and hence correction could be made before any real damage took place. Detection through the main variable, such as the'pressure in the lift pipe, is possible but often too slow to give a warning and the upset in operating conditions is so advanced when detected by observation of the main variable that damage has been done to the process and a loss has already been suffered. As an example, in a pneumatic lift operation elevating granular catalyst in a TCC (Thermofor Catalytic Cracking) system, an increase of the pressure in the lift pipe of 25 percent means that the operation has gone into an undesirable surging condition. The corresponding increase of the fluctuation in pressure is 50 percent and hence it is seen that the pressure fluctuation is a far more sensitive indicator than the pressure itself.

The object of this invention is to provide a method and means of measuring the average amplitude of a function in a process to permit this average amplitude to be used 1 for control purposes.

A further object of this invention is to measure the average amplitude of a function in a process and to use this measurement to automatically control the process to retain the amplitude substantially constant.

A further object of this invention is to provide a method and means of measuring the average amplitude of fluctuation of pressure in a process and to permit this average amplitude to be used for control'purposes.

A further object of this'invention is to provide a method and means of measuring the average amplitude of fluctuation of pressure in a pneumatic lift' elevating granular particles and to use this amplitude to control the lift operation.

FIGURE 1 is a diagrammatic representation of a TCC system with the apparatus of the invention incorporated for lift control purposes. v

FIGURE 2 is a vertical sectional view showing valve control means developed as a part of this invention.

FIGURE 3 is a diagrammatic showing of apparatus arranged in accordance with the invention to indicate average pressure amplitude.

FIGURE 4 is a simplified electronic diagram of a fluctuation detector and converter.

FIGURE 5 is the reproduction of a test recording of the pressure fluctuation in'a TCC system and the output fluctuation as indicated bythe fluctuation converter of the invention. t

FIGURE 6 is a diagrammatic showing of the complete control system for minimizing attrition damage of catalyst in a lift pipe. l

In one important aspect the invention involves the conversion of a fluctuating function from a 'process'zone, such as a fluctuating pressure, to a reasonably steady signal comparable to or related to the average magnitude of fluctuation. This reasonably steady signal can then be utilized to control the process so as tomaintain the fluctuating function under control. In a pneumatic lift, the fluctuating static pressure can be converted to a fairly steady signal which applies control to the gas flow to the lift to thereby operate the lift at maximum efficiency operation with minimum attrition. In a further aspect of the invention two streams of lift gas flowing to the lift for elevation of granular particles are converged for stabilization of temperature and pressure, one stream being responsive to flow rate control and the other stream tion of catalyst in the lift pipe in quantities large enough to be completely insupportable by the air liftwhereupon circulation stops and the blower must be shut down to empty out the lift pipe.

A pressure tap 70 is located in the upper two-thirds of the lift pipe and connectedto the indicator '79. It has been discovered that this pressure reading can be used to set the gas flow rate for minimum attrition. The gas flow is set above the refluxing rate, i.e., the rate at which violent surging or refluxing in the pipe occurs with sudden changes in pressure and a rapid increase in catalyst breakage. The gas flow is then reduced gradually by resetting the flow regulating controller 61 until the pressure, as indicated on the pressure indicator 79, shows a magnitude of fluctuation of about 100 percent. This is known as the threshold refluxing rate.

Any slight further decrease in total gas flow rate would cause the pressure in the pipe as indicated by theindicator to rise 3 or 4 times its normal value and refluxing would be present in the pipe. The fluctuation in pressure is taken from the tap 70 to a converter '79 which will be described in more detail hereinafter. This pressure fluctuation is converted by the converter to a steady signal equivalent to the average pressure fluctuation occurring in the pipe and this signal is used to: operate a controller 45. The controller 45 simultaneously opens or closes the valves 44 and 35, allowing a stream of gas to by-pass the flow rate controller 61 and the valve 62.

It is seen that this stream of gas rejoins pipe 38 just before the pipe enters the lift, and hence an additional stream of lift gas is introduced into the lift pipe to bring the total lift gas above the surge point into a region of minimum attrition. This additional stream of lift gas is pressured to a uniform pressure With the main lift gas and heated to a uniform temperature with the main lift gas. This uniform pressuring and heating avoids eddy currents in the lift pipe and other localized disturbances which would cause'a decrease in the efficiency of lift operation and an increase in the attrition.

This lift system incorporates a temperature tap 41 which is located in theupper two-thirds of the lift pipe. Prior systems used a gas temperature control near the heater 52. It was found, however, that the lift operation altered at night and this was particularly true when the air temperature dropped substantially during the night. The long lift pipe, which may extend from 100-250 ft. long, acted asa cooler to drop the gas temperature and change its density. By reading the fluctuation of temperature at tap 41, an early indication of temperature change is obtained. This temperature fluctuation is transmitted to converter 46, which is adapted to convert temperature fluctuation to'a steady signal and this signal is used to operate controller 40 and valve 39, thereby adjusting the amount of heat added to the combined streams of lift gas to maintain the gas temperature through the lift pipe substantially constant,

For control purposes it is highly desirable to have the fluctuation of pressure indicated as a substantially constant value between maximum and minimum limits.- The apparatus combination of FIGURE 3 is adapted to provide this result. The process chamber 65, which may be pneumatic lift 25 of FIGURE 1, is connected to a corn duit 66. A conduit 67 is connected to a detecting chamber 68 and has in it a unidirectional valve 69 so that fluid is permitted to flow only from the process chamber into the detecting chamber 68. A suitable apparatus combination for assuring unidirectional flow is depicted on FIGURE 2. Referring now to FIGURE 2, the conduit 52 connects to the chamber 65 and has in it a jet 53 designed to control the flow rate of the air from the chamber 65 to the chamber 68. A valve plate 54 hinged at one end 55 is adapted to close over the end of the conduit 52. A spring 56 is located between the plate 54 and a fixed bracket 57 so as to provide bias toward the closed position. A connecting rod 58 is attached to the valve 54 and extends through the body-5? of the valve.

URE 2).

A cap 66, is threaded on the end of the connecting rod 7 58 and designed to put variable tension on spring 61. By this arrangement afine adjustment of the closing pressure on the valve plate 54 can be maintained. By appropriate adjustment of the valve springs, gas will flow from chamber 65 to 68 when the pressurein the chamber 65 is suificient to open the valve, but when the pressure in the chamber 65 drops, the valve will close preventing the flow of gas from the chamber 68 to the chamber 65. By appropriate adjustment the pressure in the chamber 68 can be adjusted to substantially the maximum pressure occurring in the chamber 65. In processes of this type, unusual pressure fluctuations occur from time to time and in order to prevent chamber 68 from indicating only unusually high pressure fluctuations, a bleed orifice 62 can be located in the pipe 52 and an adjustable needle valve 63 is provided so that only a very small bleed stream of gas is permitted to transfer back from the chamber 68 to the chamber 65. This will permit the chamber 68 to compensate for unusual pressure fluctua: tions and will permit the chamber 63 to indicate generally the maximum pressure occurring in the chamber 65. This can be accomplished alternatively by a bleed linepas indicated in FIGURE 3.

Returning now to FIGURE 3, another conduit 70 is connected to the conduit 66 and also to a detecting chamber 71. In the conduit 75) is located a unidirectional valve 72 arranged to permit fluid to flow only from the detecting chamber '71 to the process chamber 65. By this arrangement the maximum pressure occurring in the process chamber will be maintained in the detecting cham ber 68 whereas the minimum pressure occurring in the process chamber will be maintained in the detecting chamber '71. it will be understood, of course, that the conduits 67 and it! could be connected directly to the process chamber as long as their connection was sufficiently close to each other. A bleed line 73 with valve 74 therein can be provided to maintain a very slight flow of gas between the chambers 68 and '71. This bleed line then replaces the separate bleed valves in the unidirectional valves 69 and 72 (such as depicted on FIG- This flow through the bleed line can be made so small that it will normally have no substantial effect upon the pressure differential maintained between the first detecting chamber and the second detecting chamber. The first detecting chamber is connected to a pressure differential transmitter 75 by means of connection 7,6 and the second detecting chamber is connected to the pressure differential transmitter by means of connection '77. This substantially cons-taut pressure differential, beinga measure of the amplitude of pressure fluctuation in the process chamber 65, can thereby be transmitted directly to a pressure recording apparatus 78 providing a substantially uniform reading. Alternatively, this pressure differential can be used to operate known apparatus for adjusting conditions in the process chamber to maintain the pressure differential substantially constant. As seen on FIGURE 1, this converter 79 is used to operate a controller 29 controlling the valves 44 and 35, which control the flow rate of the minor lift stream.

pipe, for example, is first converted'to a fluctuating volt- I age by means of a pressure transmitter, now well known in the art. For control purposes, it is highly desirable to have the fluctuation of voltage indicated as a substantially constant value between maximum and minimum limits. The fluctuation detector shown in FIGURE 4 and described below accomplishes this result. Details 8t} and 81 represent two diodes having the property of passing a flowing current in only one" direction which permits their use as unidirectional devices. Details 82 7 units. Details 34 is a high value resistor used to restrict the flow of current. Detail 855 is a very high resistance D.C. voltmeter which reads the voltage differential between capacitors 82 and 33.

A DC voltage fluctuating between say 100 and 110 volts at the rateof 3 cycles per minute, representing the pressure fluctuation of the lift pipe, is applied between the leads $6, 87. The current flows through the diode 89 which is conducting in the direction of the arrow to the capacitor 82. The positive end of the capacitor 82 is connected to the diode 80. Capacitor $2 quickly charges to the maximum potential applied between 86 87 or 110 volts. As this voltage reduces to 109 volts, diode 80 prevents the stored energy in capacitor 82 from leaking back. Diode 81 is also connected in series with capacitor 83 between the leads 86 and 87, but conducting in the opposite direction to diode 80, so that no current flows to capacitor 83. By this arrangement the maximum voltage applied between leads 86, S7 or 110 volts will be maintained in capacitor 82, whereas the minimum voltage, such as 100 volts, will be maintained in capacitor 83. The capacitor 83 receives its initial charge through a slow and gradual bleed on through diode St) and resistor 84. The balancing or drain-off resistor 84- is provided to maintain a very restricted flow of current between capacitors 82 and 83. It is apparent that without such a bleed, capacitor 82 would maintain a voltage equal to the highest voltage which had occurred in the process at some earlier time, and likewise capacitor 83 would maintain a voltage equal to the lowest voltage which had occurred in the process at an earlier time. The device would then not be indicating the present differential between the maximum and minimum voltage and would, in effect, he inoperative. The slight flow of current between capacitor $2 and capacitor 83 through resistor 84 relieves these high and low voltages, as time passes, to a level where the present voltage levels existing in the process, passing through the diodes 8t and 81, will determine the voltage in capacitors S2 and 83. This flow of current can be made so small that it will normally have no substantial immediate effect upon the voltage differential maintained between capacitor 82 and capacitor 83. A very high resistance D.C. voltmeter drawing virtually no current is connected between the positive ends of capacitors S2 and 83. This substantially constant voltage differential, being a measure of amplitude of voltage fluctuation and representing the pressure fluctuation in the process, is indicated by the voltmeter, which provides a substantially uniform reading. Alternatively, this voltage differential can be used to operate known apparatus for adjusting conditions in the lift pipe to maintain the pressure fluctuation substantially constant. Alternatively temperature fluctuation can be converted to an A.C. voltage and this converter located in place of converter 45, of FIGURE 1, to provide a fixed voltage equal.

to the amplitude of temperature fluctuation in the lift pipe 25. This voltage can then be applied to operator 4%) to position valve 37 so as to maintain the gas temperature in the lift pipe substantially constant.

Description of Reduction to Practice The method and equipment described herein were used to control a pneumatic lift elevating granular catalyst by means of an air stream. This lift had the following The apparatus was operated at optimum conditions for minimum attrition, and also at conditions of too high and too low lift air rates, both of which give excessive catalyst attrition. The following characteristics of operation for the apparatus of this invention were obtained:

Surging Lift. Air Rate,

Optimum Percent of Optimum High Velocity It can readily be seen that the pressure fluctuation is more sensitive to slight changes in operation than is the pressure itself, and that the fluctuating pressure, after being converted and amplified into a usable electrical DC. signal respectively by the pressure transmitter and the AC. amplifier, was converted into separate high and low D.C. voltages which were proportional to the amplitude of fluctuation pressure. The difference between high and low voltages has successfully been used in conjunction with a DC. amplifier and other known apparatus, such as described in US. Patent No. 2,819,121, for adjusting the lift air rate to maintain optimum conditions. The apparatus can also be used to operate the lift at any particular level of attrition where this may be desirable. it is necessary in some instances to maintain a certain level of attrition to effect removal of contaminating metals from the surface of the catalyst. This acts to restore the catalyst.

Referring to FIGURE 5, a fluctuation diagram of the pressure in the lift pipe of a commercially operating 15,000 bbl. per day TCC unit, detail 11?. shows the pressure fluctuation occurring in the lift pipe, which is used as the input to the fluctuation converter. On the same diagram detail 113 shows the output of the fluctuation converter illustrating the substantially greater magnitude of fluctuation used for control purposes. The smooth reading of the pressure fluctuation detail 112 would indicate no requirement for adjustment whereas the substantial variation in magnitude of the plot 113 indicates that considerable adjustment was necessary for superior lift performance. Of course, the pressure fluctuation occurring in the lift can be converting to any form of electrical signal and this signal can be used to control lift operation. It is preferred, however, that the fluctuation of pressure be converted to a similarly fluctuating voltage which can then be used to control lift operation.

Referring now to FIGURE 6, a complete system for controlling a pneumatic lift elevating catalyst is there shown. The two streams of lift gas are passed through conduits 5t and 29. These streams are merged and pressured by blower 51 to a constant pressure. The combined streams are heated in the heater 52. The streams are then separated in conduits 42 and 38. The main stream flow is checked by flow meter 60 and this is used to operate flow controller 61 which adjusts the valve 62 in line 38 for constant gas flow through valve 62. The streams are again combined .and introduced into lift pot 34 to elevate catalyst through the lift pipe 25. This catalyst is introduced into the lift pot 34 through pipes 32, 33.

Fluctuating lift pipe pressure is picked up at tap 70 and transferred to converter 79 where the fluctuation is converted to a steady signal. This signal is used to operate controller 45 which adjusts valves 35 and 44 to maintain a constant lift pipe fluctuation. A lift pipe temperature fluctuation is picked up at tap 41 and transferred to converter 45 where the fluctuation is converted to a steady signal, This signal is used tooperate controller 40 which adjusts valve 39 to maintain the operation of heater 52 so that the. gas temperature in the lift pipe is held constant. By this coordinated system, the lift is operated at that condition which produces minimum attrition. With any catalyst this is important. However, with certain new active catalyst, this becomes exceedingly important because the catalyst is exceedingly valuable and even levels of attrition which were previously considered tolerable are now found to be excessive; This system of automatic operation of pneumaticlifts for use in TCC or moving bed systems is, therefore, particu larly suitable for use with the new very active catalysts developed for this process.

It is within the concept of this invention to first pressure and heat the combined streams of lift gas to an advanced temperature in response to a gas temperature measurement in the upper portion of the lift pipe before splitting the gas into major and minor streams. The flow rate of the major stream is then measured and automatically controlled in response to that measurement to maintain a constant major stream flow rate which is set just above the flow rate that would cause violent surging in the lift pipe. The minor stream is then controlled automatically in response to pressure fluctuation indication obtained from the upper portion of the lift pipe and converted to a steady signal which, in turn, is used to control the flow rate of the minor stream. The minor stream is supplied with the major stream to the lift pot in a manner well known in the art and previously described to effect contact and lifting of catalyst or granular contact material through the lift as a dilute or dispersed stream of particles. The minor stream lifts the total gas flow through the lift above the refluxing level enough to provide minimum attrition. Any shift in gas flow above the level of minimum attrition is automatically compensated for by a reduction in the minor stream. Any shift in gas flow toward the point of violent refluxing is automatically compensated for by an increase in the minor stream of lift gas.

This invention has been disclosed hereinabove for use and control of a pneumatic lift and with respect to the figures provided with the application. It is understood that the invention has broader utility, and alternate uses of the invention are therefore contemplated. The only limitations intended are those found in the attached claims.

I claim:

1. In a pneumatic lift for elevating a granular contact material in a stream of lift gas the improved method of controlling the lift operation which comprises: flowing a major and minor stream of lift gas toward the bottom of the lift, measuring the flow rate of the major stream,

converging the streams of lift gas, pressuring the converged streams of gas, heating the converged streams of gas, separating the streams of gas again into major and minor streams, controlling the flow rate of the separated major stream of gas in response to said flow rate measurement, so as to maintain the flow rate of the major stream of gas substantially constant, introducing the major and minor streams of lift gas into the lower end of the lift, to elevate granular contact material, measuring the pressure fluctuation in the upper portion of the lift, converting the pressure fluctuation to a steady signal proportional to the average amplitude of pressure fluctuation,

and applying this steady signal to control the How ratev of the minor stream of lift gas as as to maintain the fluc- 'tuation of pressure in the upper portion of thelift ata substantially constant level whereby minimum attrition of the granular material passed through the lift is obtained.

if) controlling the lift operation which comprises: flowing a major and minor stream of lift gas toward the bottom of the lift, measuring the flow rate of the major stream, converging the streams of lift gas, pressuring the converged streams to a uniform pressure, measuring the lift gas temperature in the upper portion of said lift, automatically heating the converged streams of lift gas in response to said measured temperature to maintain lift gas' temperature substantially constant, separating the streams of gas once again into a major and minor stream, controlling the flowv rate of the separated major stream of gas in response to said flow rate measurement, so as to maintain the flow rate of the major stream of gas substantially constant, at a flow rate just above that of violent refluxing in the lift, introducing the major stream of lift gas into the lower end of the lift, to elevate granular contact material in dispersed form, introducing the minor stream of lift gas into the lift, to provide additional gas for elevation of granular contact material, measuring the pressure fluctuation in the upper portion of the lift, converting the pressure fluctuation to a steady signal proportional to the average amplitude of pressure fluctuation, and applying this steady signal to control the flow rate of the minor stream of lift gas, so as to maintain the fluctuation of pressure in the upper portion of the lift at a substantially constant level whereby the minimum attritionof the granular material passed through the lift is obtained.

3. In a pneumatic lift for elevating a granular contact material in a stream of lift gas the improved method of controlling the lift operation which comprises: increasing the pressure on a stream of lift gas to maintain a suitable constant lift pressure, measuring the temperature fluctuation ingthe upper portion of the lift, converting the temperature fluctuation to a steady signal proportional to the average amplitude of temperature fluctution, and automatically heating the stream of lift gas. so as to maintain the fluctuation of temperature in the upper portion of the lift at a substantially constant temperature, splitting the heated and pressured lift gas into a major and minor stream, measuring the flow rate of the major stream and automatically controlling the how rate of the major stream in response to that measurement, so as to maintain the flow rate of the major stream of gas substantially constant, at a flow rate just above that of violent refluxing in the lift, introducing the major stream of lift gas into the lower end of the lift, to elevate granular contact material through the lift in dispersed form, introducing the minor stream of lift gas into the lift, to provide additional gas for elevation of granular contact material, measuring the pressure fluctuation in the upper portion of the lift, converting the pressure fluctuation to a steady signal proportional to the average amplitude of pressure fluctuation, and applying this steady signal to control the flow rate of the minor stream of lift gas, so as to maintain the fluctuation of pressure in the upper portion of the lift at a substantially constant level whereby minimum attrition of the granular materal passed through the lift is obtained. v

4. In a pneumatic lift for elevating a granular contact material in a stream of lift gas: means for pressuring a stream of lift gas, means for heating the lift gas, a vertical lift pipe, a temperature tap in the upper portion of the lift pipe, means for converting the fluctuation of temperature to a steady signal proportional to the temperature fluctuation in the upper portion of the lift pipe, and means responsive to said signal for automatically controlling the amount of heat added to the stream of lift gas, to maintain constant lift gas temperature in therupper a portion of the lift pipe, a major gas pipe adapted to receive a major portion of the lift gas, a minor gas pipe 2. In a pneumatic lift for elevating a granular contact measuring means adapted to measure the rate of flow of the major gas stream, valve means in said major gas pipe, automaticallyresponsive to said measured gas flow, to

1 l. i 2 maintain the flow rate of the major gas stream constant, persed form through the lift pipe with minimum attria pressure tap located in the upper portion of the lift tion. pipe, means for converting the fluctuation of pressure to a steady signal proportional to the pressure fluctuation in REEQF'WWS (med in the file of this P the upper portion of the lift pipe, and valve means in said minor gas pipe responsive to said signal for auto- UNITED STATES PATENTS m i ally controlling the flow rate of the minor gas 5 313 221 g i322 r am to maintain gas fiow through the lift at the now 2,860,174 g g 1958 r q r f r min mum attrition, said major and minor 2905'538 f S r 22: 1959 g p p mm nicating with the lower end of the lift 10 3,049,380 Brennan? fg 1962 pipe, so as to elevate granular contact material in dis- 

1. IN A PNEUMATIC LIFT FOR ELEVATING A GRANULAR CONTACT MATERIAL IN A STREAM OF LIFT GAS THE IMPROVED METHOD OF CONTROLLING THE LIFT OPERATION WHICH COMPRISES: FLOWING A MAJOR AND MINOR STREAM OF LIFT GAS TOWARD THE BOTTOM OF THE LIFT, MEASURING THE FLOW RATE OF THE MAJOR STREAM, CONVERGING THE STREAMS OF LIFT GAS, PRESSURING THE CONVERGED STREAMS OF GAS, HEATING THE CONVERGED STREAMS OF GAS, SEPARATING THE STREAMS OF GAS AGAIN INTO MAJOR AND MINOR STREAMS, CONTROLLING THE FLOW RATE OF THE SEPARATED MAJOR STREAM OF GAS IN RESPONSE TO SAID FLOW RATE MEASUREMENT, SO AS TO MAINTAIN THE FLOW RATE OF THE MAJOR STREAM OF GAS SUBSTANTLY CONSTANT, INTRODUCING THE MAJOR AND MINOR STREAMS OF LIFT GAS INTO THE LOWER END OF THE LIFT, TO ELEVATE GRANULAR CONTACT MATERIAL, MEASURING THE PRESSURE FLUCTUATION IN THE UPPER PORTION OF THE LIFT, CONVERTING THE PRESSURE FLUCTUATION TO A STEADY SIGNAL PROPORTIONAL TO THE AVERAGE AMPLITUDE OF PRESSURE FLUCTUATION, AND APPLYING THIS STEADY SIGNAL TO CONTROL THE FLOW RATE OF THE MINOR STREAM OF LIFT GAS AS AS TO MAINTAIN THE FLUCTUATION OF PRESSURE IN THE UPPER PORTION OF THE LIFT AT A SUBSTANTIALLY CONSTANT LEVEL WHEREBY MINIMUM ATTRITION OF THE GRANULAR MATERIAL PASSED THROUGH THE LIFT IS OBTAINED. 